Aerodynamic Control of Long Span Bridges

Transcription

1 AEROELASTICITY Royal Aeronautica Society Monday 14 th March Aerodynamic Control of Long Span Bridges Michael Graham, David Limebeer*, Kevin Gouder and Xiaowei Zhao** Department of Aeronautics, Imperial College London. *Department of Engineering Science, University of Oxford.. **Department of Engineering, University of Warwick Acknowledgements: Konstantinos Bakis*, Yasuaki Ito, Matteo Massaro*, Martin Williams*. A

2 Active aerodynamic control of bridge deck flutter. Kobayashi and Nagaoka 1992 Fujino, Iwamoto, Ito and Hikami 1992 Wilde and Fujino 1996 Miyata 1992, 1999 Omenzetter, Wilde and Fujino 2002

3 Kinematic Model of (2-D section of) Bridge Deck fitted with Leading- and Trailing-Edge Flaps. Thin aerofoil (flat plate) potential flow theory. Theodorsen s results for a wing section + flap + tab adapted to a thin bridge section with LE and TE flaps.

4 Effect of a 15% TE flap with gain of 2.0 and 90deg phase relative to pitch (Theodorsen theory). (a) Open loop (no control) (b) Closed loop (controlled)

5 Humber Bridge

6 Great Belt Bridge (Denmark)

7 Contents of Presentation Wind Tunnel Tests of a bridge section in smooth flow and turbulence: Pitch / Heave Flutter Instability of flexibly mounted deck, Buffet forces induced by incident turbulence. Control System, Open-Loop and Closed-Loop characteristics of deck dynamics. Wind Tunnel tests of aerodynamic control effects on critical flutter speed and on turbulence buffeting. A possible passive mechanical system to implement the control system.

8 Bridge Deck Section (2 nd Forth Crossing Candidate modified with Flaps) in Imperial College Honda Wind Tunnel

9 Schematics of Bridge section

10 Bridge Deck Section in No. 5 Wind Tunnel at BMT Fluid Mechanics Ltd.

11 Deck Section and Turbulence Grid in BMT No.5 Tunnel

12 Spectrum of Vertical Velocity for Grid Turbulence compared with von Karman Theoretical Spectra.

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14 Effect of turning on LE and TE flaps under 2 nd order control with feedback from heave displacement.

15 Pitch feedback to LE Flap and Heave feedback to TE Flap

16 Application of Strip Theory for Buffet Loading and Response. (Massaro and Graham, J Fluids & Structures 2015)

17 Theoretical Admittances of Lift for Rigid Bridge Section in Grid Turbulence.

18 Theoretical and Measured Lift Spectra for Rigid Bridge Deck in Grid Turbulence.

19 Theoretical and Measured Heave and Pitch Spectra, Flexibly Mounted Bridge Deck in Turbulence (Subcritical wind speed).

20 Block Diagram of Control System (s = Laplace transform variable) Feed Back Plant Gain White Noise Heave and Pitch Response Aerodynamics Von Karman Filter Theodorsen Circulation Function

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22 Root Loci of Open Loop System (wind speed swept from 5m/s[blue] to 25m/s[red]

23 Open Loop Damping Ratio measured for Supercritical Free Stream Speeds (without Turbulence).

24 Root Loci using 3 rd Flutter Controller

25 Damping ratio versus free stream velocity for different controller gains, TE flap only with pitch feedback.

26 Measured Damping Ratios with 3 rd Flutter Controller, LE and TE flaps

27 LES computed flow over bridge section. (Y. Ito)

28 Measured (Static) Aero Derivatives of Lift and Moment for Deck dcl/da = -5.2 dcm/da = 2.6

29 Comparison of Measured and Theoretical Unsteady Lift and Pitching Moment Derivatives dl/dh dl/da dl/da dm/dh dm/da dm/da

30 Theoretical Mean Square Pitch and Heave Responses in Turbulence (Open Loop and Closed Loop Flutter Controllers) Open Loop Open Loop Closed Loop Closed Loop (a) Pitch (b) Heave

31 Buffet Suppression by TE flap (Buffet optimised controller).

32 Measured RMS Reductions in Pitch and Heave when closed-loop flap buffet control is applied.

33 Part Span lengths of deck during erection.

34 Schematic of Mechanical ( Passive ) Feedback Control

35 Concluding Remarks Substantial increases in flutter speed and significant suppression of buffet loads on bridge decks are possible using active, distributed flap control. Both leading edge and trailing edge flaps can contribute, but in practice there are important separation issues associated with sharp edged leading edge flaps and rounding trailing edges of flaps reduces effectiveness, (a problem for bridges if extreme winds from either side). A purely mechanical system (under evaluation) can replace electronic control and input power actuation.